1. Field of the Invention
The present invention relates to a shaping control method and a shaping control apparatus for controlling a transfer rate of packets so that the transfer rate does not overrun a predetermined reference rate.
2. Related Background Art
In packet communication, control called as a shaping for maintaining the transfer rate within the reference rate that vendors set is performed to improve use efficiency of lines, so that the transfer rate does not overrun a predetermined limit.
As conventional techniques, there is provided with a method for determining in advance a time slot to transfer the packets and managing by e.g. a list, which is called as a time slot ahead determining method, and a method for scanning information of all elements before the transfer time of the packets and determining whether or not to be able to transfer them by each scan, which is called as a method of scanning at transfer time.
The time slot ahead determining method calculates a transfer-able time of the connections that the packets belong, and inserts the packets into the list in which the packets are arranged in transfer order. In case of this method, the arriving order of the packet is generally different from the transfer order of the packet. Because of this, if necessary, a processing which scans the already lined-up elements and sorts them in transfer-able time order is required. Accordingly, in order to correctly set the transfer order, it is necessary to scan all the elements and compare a theoretical transfer time of each element with each other.
However, because there is a limit for the number of times of access for hold means memorizing the elements, the number of the elements which can scan in transfer cycle of the packets is limited. Accordingly, it is difficult to perform the shaping for large amount of connections with a high degree of accuracy.
On the other hand, because the method of scanning at transfer time scans the elements transfer-able from all the elements, it is possible to take e.g. conditions of a physical layer that the connections are connected into account. However, the condition of the physical layer changes by each packet, and a time when the packets of the connections with high speed rate are held in the hold means is short. Because of this, it is necessary to scan all the elements at each packet cycle in order to perform the high-precision shaping. However, as described above, because there is a limit to the number of times of access for the hold means, it is difficult to perform the shaping for large amount of connections with a high degree of accuracy.